Drought tolerance is a complex trait, controlled by multiple genes. Gene switches such as transcription factors, which can have significant and specific effects on plant physiology, are desirable modulation targets. Stress-responsive NAC transcription factors (SNACs) may control expression of numerous downstream genes important for adaptation to drought stresses and may ultimately enhance drought tolerance through one or more mechanisms such as stomatal aperture reduction, delayed senescence, and increased sink and source strength. It has been shown that ABA- and drought-responsive NACs can enhance drought tolerance in Arabidopsis (Tran, et al., (2004) Plant Cell 16:2481-2498) and rice (Hu, et al., (2006) PNAS 103(35):12987-12992). Therefore, SNAC genes from maize may also be used individually or in combination with other genes to enhance drought tolerance.
Expression of heterologous DNA sequences in a plant host is dependent upon the presence of operably linked regulatory elements that are functional within the plant host. Choice of the regulatory element will determine when and where within the organism the heterologous DNA sequence is expressed. Where continuous expression is desired throughout the cells of a plant, and/or throughout development, constitutive promoters are utilized. In contrast, where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. Where expression in specific tissues or organs is desired, tissue-specific or tissue-preferred promoters may be used. That is, they may drive expression exclusively or preferentially in specific tissues or organs. Such tissue-specific promoters may be temporally constitutive or inducible. In any case, additional regulatory sequences upstream and/or downstream from a core promoter sequence may be included in expression constructs of transformation vectors to bring about varying levels of expression of heterologous nucleotide sequences in a transgenic plant.
As this field develops and more genes become accessible, a greater need exists for plants transformed with multiple genes. These multiple exogenous genes typically need to be controlled by separate regulatory sequences. Further, some genes should be regulated constitutively whereas other genes should be expressed at certain developmental stages or locations in the transgenic organism. Accordingly, a variety of regulatory sequences having diverse effects is needed.
Multiple regulatory sequences are also needed in order to avoid undesirable molecular interactions which can result from using the same regulatory sequence to control more than one gene.
The inventor herein discloses the isolation and characterization of a promoter associated with a transcription factor which can serve as a regulatory element for expression of isolated nucleotide sequences of interest, thereby impacting various traits in plants. Alternatively or additionally, the promoter may be used to drive scorable markers.